Heat protected pitot-static tube



Nov. 12, 1940. P. KOLLSMAN HEAT PROTECTED PITOT STA'I IC TUBE FiledMarch 12, 1938 3 Sheets-Sheet l W mm m TL N W R vK am N T A U H B 7 1 16 1 1 9 0 1 8 0 1 Nov. 12, 1940. P. KOLLSMAN HEAT PROTECTED PITOT STATICTUBE Filed March 12, 1938 3 Sheets-Sheet 2 INVENTOR PHUL KULLSMHN BY Z2ATTORNEY A IIIIIII ll NOV. 12, 1940. P KOLLSMAN 2,221,547

HEAT PROTECTED PI'IOT STATIC TUBE 'Filed March 12, 1938 3 Sheets-Sheet 3111 Y RELFIY BHTTERY u W w INVENTOR PHUL KULLSMFIN B ATTORN EY PatentedNov. 12, 1940 UNITED STATES- PATENT OFFICE 2,221,547 HEAT PROTECTEDerror-swarm TUBE Application March 12, i938, Serial No. 1%,i65

8 Claims. ((71. 73-212) This invention relates to Pitot-static tubes ofthe type adapted for use with airplanes for the determination of the airspeed, oi the craft and relates particularly to heating systems forkeeping the Pitot-static tubes free from ice, snow and sleet.

The prevention of the accumulation oi ice upon and in the ports of sucha tube is vital for its proper functioning. In an electrical heatingsystem for Pitot-static tubes injuries may occur to the heating element,thus requiring frequent replacement of the heater. Accordingly provisionfor opening and closing the tube is neces sary ior replacing the heatingelement which may lead to weaknesses in. the tube structiu'e. Under myinvention I prefer m integral, streamlined metallic tube or shell :lorthe Pitct static tube proper, within which i provide part of a heatingsystem having automatic provisions capable of supplying heat,conductively transferred throughout the Pitot-static tube to me vent theformation of ice and, in addition so controlled as to preventover-heating and the burning out of the heater even the air ex posuretemperature to which the tube is subjected be relatively high.

In aerial navigation, particularly under conditions of fog, ice andsnow, an air speed indicator is an essential instrument from which tocom pute distance traveled by a dead. reckoning procedure. But underconditions of fog, snow and ice, particularly at temperatures close tothe freezing point, the Pitot-static tube portion of the indicator tendsto fill with ice and snow and to fall of functioning. In order to avoidthis failure, it is customary to provide an electric heater adjacent theentrance end of the dynamic pressure duct, which serves to raise thetemperature of the Pitot-static tube above the melting point of ice,thereby preventing adherence of congealed water to the exterior tubesurfaces and melting out any congealed moisture which may enter thedynamic pressure duct. Difiiculty is, however, experienced with suchheaters in maintaining them in operative condition because of the lowamount of heat which can be dissipated from the tube structure duringnon-flying periods and the relatively much larger amount of energyrequired to function for adequate heating during flight intervals. Thatis, with a plane on the ground in summer weather, a heat energyconversion in the heater of more than a very few watts will overheat theheater and burn it out, whereasin flight under icing conditions, aminimum of about watts is required to keep the tube free of ice. Thisrequires that the heater he switched on when icing conditions occur andswitched ofi before landing, else the heater will 4 be burned out andinoperative for the next ascent and the air speed meter may fail forthis 5 reason. Furthermore, a heater control ice the tube under thepilots hands is highly objection able item, since it is another thing toburden the memory of a pilot already overloaded and the necessity ofprotecting the tube heater may re suit in neglect of some other moreimportant iu= strurnent or control, with consequent accident or in attaning object of safeguarding heater, I propose provisions, either one 01N which is local temperature controlled switch in the circuit or" theheater may be einploy-ed to out ch current supply when the temperatureof the tube and of the heater ap- A preaches an unsafe maximum and toturn it on wh n the temperature of the tube approaches an undesirableminimum. (I prefer to turn on current at a drop oi temperature below itC. and to cut ofi the current at 20 C.)

The present invention provides means ior the automatic protection of thePitot tube an er by the supply to the tube of suflicieut h at energyduring intervals of flying at low temperatures and cuts oh the energysupplied to the heater during nonuiylng intervals and during dying atsafe temperatures through "the operation, individually or simultaneouslyof a pressure actuated switch responsive to dynamic air pressures and ofa temperature responsive mechanism which is actuated by the ambient airtemperature surrounding the Pitot-static tube, the dynamic duct thereinor the airplane itself.

Objectively my invention eflects a saving in expended heater energy,lower maximum temperature at a standstill of a plane when the heatercircuit is left on and the elimination of replaceable heater units.

The invention further provides a special type of relay operating inconjunction with a temperature responsive or pressure-responsive member,simultaneously or one at a time, in conjunction with a heater memberadjacent the dynamic duct of a Pitot-static tube.

An object of the invention thus is to turn on a Pitot-static tube heaterautomatically during intervals of flying at low temperatures and to turnit oil during intervals of flying at safe temperatures.

Another object of the invention is to turn on a Pitot-static tube heaterduring flying intervals and to turn it off during non-flying intervals.

Still another object of the invention is to turn on a Pitot-static tubeduring flying intervals at low temperatures and to turn it of! duringnon-flying intervals and during flying intervals at safe temperatures.

Still another object of the invention is to relay-control the heatercurrent to a Pitot-static tube heater.

Yet another object oi the invention is to relay-control the heatercurrent to a Pitot-static tube heater by the combined action of apressuresensitive and temperature-responsive mechanism.

Still a further object of the invention is to shut off automatically theheater current during nonfiying intervals, to shut off the heatercurrent automatically during flying at safe temperatures and to permit ashutting off of the heater current manually during intervals when theheater is not needed, particularly when the plane is laid up out ofservice.

Other objects and structural details of the invention will be apparentfrom the following description when read in connection with theaccompanying drawings, wherein:

Fig. 1 is a view in side elevation, partly in section, of an airplanefuselage equipped with the Pitot-static tube and protecting members ofthe device'of the invention;

Fig. 2 is a View in vertical section of the Pitotstatic tube and heatermember of Fig, '3

Fig. 3 is a diagrammatic View of the heater, heater circuits andprotecting mechanism of the embodiment of Figs. 1 and 2;

Fig, 4 is a side view, partly in section, of an airplane fuselageequipped with an alternative form of the Pitot tube protectingmechanism;

Fig. 5 is a diagrammatic view of the tube and protecting mechanism ofthe embodiment of Fig. 11;

Fig. 6 is a diagrammatic view of circuits and apparatus of still anotherembodiment of the invention;

Fig. 'l is a diagrammatic view of circuits and apparatus of anotherembodiment of the invention.

In the embodiment of the invention shown in Figs. 1, 2 and 3 the heatsensitive member is placed within the Pitot-static shell to control arelay having heavy, rugged contacts mounted in a position where thecontacts are readily reached for maintenance. As shown in Fig. l, theairplane fuselage ifll has mounted thereon a strut member I02 carryingthe shell Ill, with- 'in which there is mounted the dynamic duct I IIIof the Pitot tube structure. The shell I03 serves as the static pressuremeans, from which the static pressure at any given elevation is conveyedthrough a tube member I" to instruments which require an accurate staticpressure, such as the sensitive altimeter and the air speed indicator.Simultaneously, the dynamic pressure from the duct I is conveyed througha tube I08 to the air speed indicator I01 and such other instruments asutilize the dynamic pressure, mounted upon the instrument board. Aheater member I" is mounted within the streamlined Pitot-static shell Iadjacent the dynamic duct I for the purpose of supplyin heat thereto insumcient quantities to prevent the formation and attachment of ice tothe inner and outer surfaces of the tube and shell. Also within theshell I there is provided a temperature-responsive member Hi9, which mayconveniently be a strip of the brass-invar steel material, well known asbi-metal." A source of heating energy ill such as a battery or a powerdriven generator is provided and connected, as shown in Fig. 3, to theheater I08 by appropriate leads H2 and Hi, the circuit passing throughthe contacts ill of a relay Iii. The bi-metal I" has an attached con-'tact H6 which cooperates with a second contact I I1. These contacts areconnected in circuit with the winding of the relay I it.

As long as the temperature of the ambient air through which the plane isflying is above freezing or above a temperature of about 40 degreesFahrenheit, the bl-metal member I09 holds the contacts H6 and H1separated, open-circuiting the relay H5 and leaving the relay contactsIll open, thereby preventing the flow of current through the heater I08.When, however, the temperature of the ambient atmosphere falls muchbelow about 40 degrees, thereby approaching icing temperatures, thebi-metal I" closes the contacts 6 and H1, energizes the relay Hi fromthe current source Ill, thereby closing the contacts Ill and energizingthe heater Thus, it will be observed that while thetemperature-responsive member is positioned within the shell of thePitot tube, the duty required of the control contacts is so much reducedand so light that failures practically never occur and the heavier dutyimposed upon the heater circuit contacts is readily carried since therelay contacts are convenient of access. Thus, the device of theinvention provides a highly rugged automatic control for the heatermember in a Pitot tube structure.

This type of automatic heater thus removes from the pilot's memory andconsciousness all necessity for paying attention to any controls for themaintenance of his air speed indicator in operating condition. contactsare readily accessible for servicing by the ground crew, and the heatercurrent is turned on automatically as soon as possible icingtemperatures are reached and remains turned on until the temperaturerises above the icing point. In addition, the pilot may land without thenecessity of attention to the air speed indicator, and may land fullyassured that the heater will not be inlured by excess power oroverheating and with the assurance that the heater will be ready forimmediate service at the next flight.

It is not necessary that the temperatureresponsive elements be in theimmediate neighborhood of the Pitot tube since it is the temperature ofthe atmospheric air which determines whether the heater current shall beon or ofl and not the actual temperature of the Pitot tube. Accordinglythe structure of Fig. 'I may be utilized as an alternative embodimentwhich will be described later.

The presenceof an air stream above some threshold velocity-past thesurface of the Pitot tube will insure the safety of the heater memberagainst bum-out and accordingly, the heater member may be turned on assoon as flying speed is reached and may remain turned on until a landingis made.

For this purpose the embodiment shown in Figs. 4 and 5 may be utilized.In this embodiment the same strut member ll! attached to the fuselage I"may be utilized with the Pitot shell I03 and dynamic duct I therein.Branch pipes I24 and I! may be led from thedynamic duct The powercircuit control access? I06 and the static duct I05 to the pressureresponsive member I26.

The pressure-responsive member tilt may contain a pressure actuatedcapsule l2"! connected to the dynamic duct I06 and the casing oi themember I26 may be connected to the static duct I05 and shell I03.Adjacent the capsule 1320 there are provided contacts l28 which areconnected. in the coil circuit of the relay H5, as shown in Fig. 5. Anauxiliary hand switch ltilmay be connected in series with the contactsI28, to com plete the relay coil circuit. The heater member I08 isconnected to the power source It 5 through l elaids, asshown, andthrough the relay contacts Inthe operation of this embodiment, the handswitch I20 may be closed at any convenient time, but the contacts I28remain open until speed is obtained and the dynamic pressure built up inthe duct I04 to such a value as to expand the capsule H1 and therebyclose the contacts I28, thus closing the coil circuit of the relay lit,and attracting its armature to close the contacts IM. This permitscurrent to flow in the heater I08, which will continue as long as flyingspeed is maintained, or until the switch 22s is opened by hand. If theswitch I29 is not opened by hand but the plane lands, the loss of flyingspeed reduces the pressure in the capsule 521 and there by opens thecontacts 528 to de-energize the relay H5, open its-contacts H4 andole-energize the heater I08, thereby preventing a burn-out.

Thus, since flying speed provides an air stream over the Pitot-statictube shell structure suili ciently great to removefrom it any excessamount of heat which might injure the heater, the heater may beenergized during all flying periods, under the control of the dynamicpressure in the cap=- sule I21, thus likewise freeing the pilot from thenecessity of remembering his Pitot tube heater to make sure that itfunctions when needed and; does not burn out. That is, a fullysatisfactory protection of the tube and of the heater is obtainable bythe simple feature of dynamic pres sure control of the heater powersupply circuit.

In some instances it may be desired to conserve the electrical energysupply to the utmost, such as during flying in Arctic regions where thenor= mal ground temperatures may on occasion be below freezing. Theembodiment oi Fig. 6 provides this function by a combination of temperature-sensitive control and pressure control.

As shown in Fig. 6, a similar Pitot-static tube structure is providedconsisting of a similar shell I03 housing a dynamic duct I04, adjacentto which is a similar heater I08, the whole structure being mounted inany desired way, such as upon a strut of the same kind as the strut E02shown in Fig. 1. .A pressure responsive capsule I2! is provided andconnected to respond to the dynamic pressure in a manner similar to thecap sule shown in Fig. 4. In addition the capsule may also be acted uponby the static pressure, as hereinbefore described. The capsule I27 oper=ates the contacts I28 for the control of current in the relay coil H5. Atemperature-responsive member, which may be a bi-metal strip I09,actuates the contacts H6 and Ill. These con= tacts are connected inseries wi h the contacts I28 and the relay coil H5, the entire circuitbeing energized by the power supply Ill. relay contacts I are closed bythe relay when both contacts II6-I I! and contacts I28 are closed,thereby supplying heater power from the power supply III to the heaterI08.

The

in the operation of this embodiment of the invention, the heat-sensitivemember Hi9 will close the contacts lid-H2 when the termperatureapproaches the freezing point, or goes below. But the relay circuit isnot closed until flying speed is obtained which provides suflicientdynamic pressure to actuate the capsule iii and close the contacts we.Thus, if in flight a ternperature safely above the icing point isreached, the contacts l lG--i i? open, which opens the relay circuit andthereby opens therelay contacts to disconnect the power supply to theheater @033, without regard to the presence or absence of flying speed.Similarly, if the plane lands, the

- lack of dynamic pressure opens the contacts i233,

similarly disconnecting he heater power from the heater without regardto the ambient temperature.

Thus, this embodiment oi. the invention pro vides a automatic control ofthe Pitot tube heater which not only protects the heater and the airspeed indicator readings, but conserves the utmost possible heatingpower.

It is of course not n cessary that the ternperature-responsive member bepositioned in the Pitot tube shell structure. It may be insteadpositioned at any convenient point which par-= takes of the temperatureof the air through which the plane is flying, as is shown in Fig. I.

The embodiment of Fig. 7 utilizes a similar static shell member E03supported upon a com venient strut, of the type shown in Fig. l. Theshell 903 contains the dynamic duct 504 and heater @08. The capsule tilis responsive to the dynamic pressure, as previously described, for theoperation of the contacts 528 which are con nected as previouslydescribed in connection with Figs. 4 to 8. The temperature-sensitivemember 625 is placed in any convenient position where it will partake ofthe normal ambient air tempera ture, and the contacts 622 controlled bythe temperature-responsive member l2i are connect ed in series with thecontacts H28 in a manner analogous to that of the embodiment of Fig. 6.,for the control of the relay H5 and its contacts lit, which turns thecurrent on and ad to the heater Hit.

The operation oi this embodiment is closely similar to the operation ofthe embodiment of Fig. 6.

Thus, the device of the invention provides a simple system for thecontinued protection or an air speed indicator system, in which a heateris provided for preventing the accumulation of ice, snow and sleet inand upon a Pitot-static tube structure and in which the heater member isfully protected against the danger of burn-out without burdening thepilots memory or hands with controls and the necessity of operating themto turn the heater current on during icing conditions and to turn it offupon landing.

While there are above disclosed but a limited number of embodiments ofthe device of the invention, it is possible to provide still other combodiments without departing from the inventive concept herein disclosedand it is therefore desired that only such limitations be imposed upon.the appended claims as are stated therein.

What I claim and desire to secure by United States Letters Patent is:

l. The combination with a Pitot-static tube for aircraft having metallicstatic and dynamic pressure ports; of an electric heating elementarranged to heat said ports; and means responsive to the speed of thecraft for controlling a flow oi electrical energy to said heatingelement.

2. The combination with a Pitot-static tube having metallic static anddynamic pressure ports; oi an electric heating element arranged to heatsaid ports; and means responsive to a diii'erence in pressure betweensaid static and said dynamic pressure ports for controlling a flow ofelectrical energy to said heating element.

3. The combination with a Pitot-static tube having metallic static anddynamic pressure ports; of an electric heating element arranged to heatsaid ports; and pressure responsive means connected to said dynamicpressure port for controlling a flow of electrical energy to saidheating element.

4. The combination with a Pitot-static tube having metallic static anddynamic pressure conduits; of an electric heating element arranged toheat said conduits; a. switch connected to control a flow of electricalenergy to said heating element; and a pressure responsive meansresponsive to the pressure in said dynamic pressure conduit, saidpressure responsive means being connected to actuate said switch.

5. The combination with a Pitot-statlc tube having metallic static anddynamic pressure ports; of an electric heating element arranged to heatsaid ports; a switch connected to control a flow 01' electrical energyto said heating element; and a diaphragm responsive to a difference inpressure between said static and said dynamic pressure ports, saiddiaphragm being connected to operate said switch.

. 6. The combination with a Pitot-static tube including a metallic shellmember having static and dynamic pressure conduits therein; 01 anelectric heating element arranged to heat said shell a relay including awinding and an armature, the armature being connected to control a flowof electrical energy to said heating element a switch connected tocontrol a flow oi electrical energy to said winding; and a diaphragmresponsive to a diflerence in pressure between said static and I saiddynamic pressure conduits, said diaphragm being connected to opeartesaid switch.

7. The combination with a Pitot-static tube including a metallic shellmember having static and dynamic pressure conduits therein; oi anelectric 10 heating element arranged to heat said shell; a relayincluding a winding and an armature, the armature being connected tocontrol a flow oi electrical energy to said heating element; a tem-.

perature responsive first switch within said shell; 15

said static and said dynamic pressure conduits, I.

said diaphragm being connected to operate said second switch.

8. The combination with a Pitot-static tube having metallic static anddynamic pressure conduits; of an electric heating element arranged to 5heat said conduits; a relay including a winding and an armature, saidarmature being connected to control a flow of electrical energy to saidheating element; a temperature responsive first switch responsive tochanges in temperature of the atv mospheric air;v a second switch, saidfirst and said second switch being connected jointly to control a flowof electrical energy to said winding; and a diaphragm responsive to adifference in pressure between said static and said dynamic pressureconduits, said diaphragm being con nected to operate said second switch.

* PAUL KOLLSMAN.

